Power inductor structure

ABSTRACT

A variety of power inductor structures are obtained by arranging a magnetic material block between a plurality of wires and a plurality of bond fingers or bond finger pairs. The power inductor structure can provide high inductance and high currents and at the same time afford smaller sizes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an inductor structure, and moreparticularly to a power inductor structure.

2. Description of Related Art

In general, power inductors function by taking energy from theelectrical circuit, storing the energy in a magnetic field and returningthis energy to the electrical circuit. For electronic products, powerinductors are frequently used as DC-to-DC converters or applied in powermanagement circuits.

However, common surface mount type (SMT) power inductors are notsuitable to be designed as parts of the package modules because theseSMT power inductors are huge in sizes and expensive in costs. On theother hand, RF chip inductors may be compact in sizes but theseinductors can not provide high inductance or endure large currents asrequired.

Hence, it is desirable to develop power inductors with smaller sizes,lower costs, high inductance and required current capability at the sametime.

SUMMARY OF THE INVENTION

In view of the foregoing, the present invention provides a powerinductor structure, which offers high inductance and high currents. Thepower inductor structure of the present invention also affords smallerpackage sizes at lower fabrication costs.

The present invention is directed to a power inductor structureincluding a package substrate having a metal layer disposed thereon, amagnetic material block and a plurality of wires. The metal layerincludes a plurality of individual bond fingers and each bond fingerconsists of two separate widen portions and a connecting portion locatedbetween the two widen portions. The magnetic material block is locatedon the package substrate, above the connecting portions and between thewiden portions, while the plurality of wires, located over the packagesubstrate and across the magnetic material block, electrically connectsthe plurality of the bond fingers.

The present invention further provides a power inductor structure. Thepower inductor structure includes a package substrate having a firstmetal layer and a second metal layer respectively disposed on a twoopposite surfaces of the package substrate, a plurality of conductivevias located within the package substrate, a magnetic material blocklocated on the package substrate and a plurality of wires. The firstmetal layer comprises a plurality of bond finger pairs, while the secondmetal layer comprises a plurality of conductive lines. Each bond fingerpair consists of two separate widen portions, and the two widen portionsof each bond finger pair is electrically connected through theconductive vias and one conductive line. The plurality of wires, locatedover the package substrate and across the magnetic material block,electrically connects the plurality of the bond finger pairs.

According to embodiments of the present invention, a dielectric core ofthe package substrate includes a slot located beside the magneticmaterial block and between the widen portions and the magnetic materialblock.

According to embodiments of the present invention, the slot can bering-shaped and surround the magnetic material block.

According to embodiments of the present invention, a dielectric core ofthe package substrate may include a trench and the magnetic materialblock is disposed within the trench of the dielectric core. The magneticmaterial block is protruded from the trench and is higher than a topsurface of the package substrate.

According to embodiments of the present invention, the power inductorstructure may further include two adhesive layers respectively disposedon both opposite surfaces of the magnetic material block to enhance theadhesion.

In order to the make the aforementioned and other objects, features andadvantages of the present invention comprehensible, several embodimentsaccompanied with figures are described in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic top view showing a power conductor structureaccording to the first embodiment of the present invention.

FIG. 1B is a schematic cross-sectional view showing the power conductorstructure of FIG. 1A.

FIG. 1C is an example showing the arrangement of the bond fingers of thepower conductor structure.

FIG. 2A is a schematic top view showing a power conductor structureaccording to the second embodiment of the present invention.

FIG. 2B is a schematic cross-sectional view showing the power conductorstructure of FIG. 2A.

FIG. 2C is a schematic 3-D view showing a portion of the power conductorstructure of FIG. 2A from the bottom surface.

FIG. 3A is a schematic top view showing a power conductor structureaccording to the third embodiment of the present invention.

FIG. 3B is a schematic cross-sectional view showing the power conductorstructure of FIG. 3A.

FIG. 4A is a schematic top view showing a power conductor structureaccording to the fourth embodiment of the present invention.

FIG. 4B is a schematic cross-sectional view showing the power conductorstructure of FIG. 4A.

DESCRIPTION OF EMBODIMENTS

Reference will now be made in detail to the present preferredembodiments of the invention, examples of which are illustrated in theaccompanying drawings. Wherever possible, the same reference numbers areused in the drawings and the description to refer to the same or likeparts.

The inductor structures or related modifications described in thepresent invention can be applied for general types or high frequencypackage modules. As described hereinafter, the embedded inductorstructures refer to the inductor structures at least partially embeddedor set in the wiring board or printed circuit board of the packagemodules. However, certain embodiments of the power inductor structuresmay be configured to be exactly on the package substrate or the wiringboard, and are nonetheless included within the scope of this invention.

The inductor structures as described in the present invention takeadvantages of the wire-bonding technology, and the applied materials arecompatible with the currently used packaging materials. Hence, thefabrication costs of the power inductor structures according to thepresent invention are lower, when compared with the conventional powerinductors.

FIG. 1A is a schematic top view showing a power conductor structureaccording to one embodiment of the present invention. FIG. 1B is aschematic cross-sectional view along line I-I′ showing the powerconductor structure of FIG. 1A.

According to the embodiments of this invention, the package substrate100 can be a wiring board, such as two-layered or four-layered printedcircuit board (PCB), or a laminate board. In FIG. 1A, the packagesubstrate 100 is a two-layered PCB having at least a top metal layer 100b disposed on the dielectric layer 100 a. The top surface 10 a of thepackage substrate 100 having a plurality of bond fingers 102, arrangedin parallel and physically separate from one another. Depending on thedesign requirements, the number of the bond fingers 102 is N, where N isa positive integer, larger than three. Each bond finger 102 consists oftwo widen portions 102 a located at two sides and a connecting portion102 b located in-between and connecting the two widen portions 102 a.FIG. 1C is an example showing the arrangement of the bond fingers 102.However, the shape and arrangement of the bond fingers 102 are notlimited by the example provided herein and may be modified based on theconsiderations of compactness and electrical properties. In addition tothe bond fingers 102, connection traces 104 can be arranged beside themost peripheral bond fingers 102 for electrical connection to externalcircuits or components. The bond fingers 102 and the connection traces104 can be fabricated by patterning the top metal layer 100 b of thepackage substrate 100. The material of the top metal layer 100 b can becopper, for example.

Taking advantages of the wire-bonding process of the packagingprocesses, a plurality of wires 106 are formed between the bond fingers102 as well as between the bond fingers 102 and the connection traces104, as shown in FIG. 1A. The material of the wire 106 can be copper,for example. Besides connecting the connection traces 104 and the bondfingers 102, each wire 106 connects one widen portion 102 a of the bondfinger 102 and another widen portion (i.e., the widen portion located atthe other side) of the next bond finger 102. In this case, although eachbond finger 102 is physically separate from one another, each bondfinger 102 is electrically connected to its most adjacent bond finger(s)102 and/or its most adjacent connection trace 104. Through suchelectrical connection arrangements of the wires and the bond fingers,the continuous coil is obtained.

Within the distribution region D of the bond fingers 102, a magneticmaterial block 108 is disposed over the package substrate 100, above thebond fingers 102 and below the wires 106. The magnetic material block108 is located between the widen portions 102 a and located right abovethe connecting portions 102 b. Preferably, two adhesive layers 110 arerespectively disposed on both opposite surfaces of the magnetic materialblock 108 to enhance the adhesion between the magnetic material block108 and the bond fingers 102 or between the magnetic material block 108and the wires 106. The material of the magnetic material block 108 canbe a conductive material, such as nickel or ferrites, for example. Theadhesive layer 110 can be a non-conductive epoxy layer or anon-conductive adhesive film, for example.

FIG. 2A is a schematic top view showing a power conductor structureaccording to another embodiment of the present invention. FIG. 2B is aschematic cross-sectional view along line I-I′ showing the powerconductor structure of FIG. 2A. FIG. 2C is a schematic 3-D view showinga portion of the power conductor structure of FIG. 2A from the bottomsurface.

In this embodiment, features similar to or the same as the aboveembodiment will not be described in details. In FIG. 2A, the packagesubstrate 200 is a two-layered PCB having at least a top metal layer 200b and a bottom metal layer 200 c respectively disposed on two oppositessurfaces of the dielectric layer 200 a. The top metal layer 200 b of thepackage substrate 200 includes a plurality of bond finger pairs 202 onthe top surface 20 a, while the bottom metal layer 200 c includes aplurality of conductive lines 205 on the bottom surface 20 b.Alternatively, if the package substrate 200 is a four or more-layeredPCB, the bottom metal layer can be any inner metal layer of the multiplelayers of the PCB.

Different from the above embodiment, each bond finger pair 202 consistsof two separate widen portions 202 a located at two sides of themagnetic material block 208. Depending on the design requirements, thenumber of the bond finger pairs 202 is N, where N is a positive integer,larger than three. The shape of the widen portion 202 a is not limitedto the ellipse, but could be round, square, or any polygonal shape. Asshown in FIG. 2C, the two separate widen portions 202 a of each bondfinger pair 202 are connected through conductive vias 203 inside thedielectric layer 200 a and one conductive line 205 on the bottom surface20 b of the package substrate 200. The vias 203 and the conductive lines205 are considered comparable to the connecting portions 102 bconnecting the two widen portions 102 a in the above embodiment. In thisembodiment, such arrangement may be more space economical and provideflexibility in design. Similarly, the shape and the arrangement of thebond finger pairs 202 are not limited by the examples provided hereinand may be modified based on the considerations of compactness andelectrical properties. In addition to the bond finger pairs 202,connection traces 204 can be arranged beside the most peripheral bondfinger pairs 202 for electrical connection to external circuits orcomponents.

As shown in FIGS. 2A-2B, a plurality of wires 206 are formed between thewiden portions 202 a of the bond finger pairs 202 as well as between thewiden portions 202 a and the connection traces 204. In FIG. 2A, the wire206 is arranged across the magnetic material block 208 and connects onewiden portion 202 a of the bond finger pair 202 (i.e. at one side of themagnetic material block 208) and another widen portion 202 a (i.e., thewiden portion located at the other side of the magnetic material block208) of the next bond finger pair 202. That is, the two separate widenportions 202 a of the same finger pair 202 is electrically connectedthrough the vias 203 and the conductive line 205 as shown in FIG. 2C,while each bond finger pair 202 is electrically connected to its mostadjacent bond finger pair(s) 202 and/or its most adjacent connectiontrace 204 through the wires 206. Through such electrical connectionarrangements of the wires, the embedded vias, the conductive lines andthe bond finger pairs, a continuous coil is obtained. For the continuouscoil, the number of the bond finger pairs 202 N is the number of theturns of the coil.

The magnetic material block 208 is disposed on the top surface 20 a ofthe package substrate 200, between the two widen portions 202 a of thebond finger pairs 202 and below the wires 206. Preferably, one adhesivelayer 210 is respectively disposed on both opposite surfaces of themagnetic material block 208 to enhance the adhesion between the magneticmaterial block 208 and the substrate 200 or between the magneticmaterial block 208 and the wires 206.

Alternatively, slots can be designed beside or surrounding the magneticmaterial block. As shown in FIGS. 3A-3B, a ring-shaped slot 312 islocated within the dielectric layer 300 a of the package substrate 300and surrounding the magnetic material block 308. The slot 312 is builtinto the dielectric layer 300 a as well as between the bond finger pairs302 and the magnetic material block 308 without lowering the position ofthe magnetic material block 308, when compared with FIG. 2A. The slot312 can be arranged along the four sides of the magnetic material block308, or along any two opposite sides of the magnetic material block 308,for example. The depth or the shape of the slot 312 can be adjustedaccording to the electrical properties or layout requirements. Thequality factor (Q) of an inductor is the ratio of its inductivereactance to its resistance at a given frequency, and is a measure ofits efficiency. The design of the slot in the power inductor structurecan offer high quality factor. Hence, the power inductor structuredesigned with the slot has high imaginary impedance due to low tangentloss involving replacing the dielectric material with air (i.e. theformation of the slot).

Moreover, in the following embodiment, trenches can be formed in thepackage substrate and the magnetic material block can be embedded moredeeply, so as to either reduce the height of the package module or toprovide larger magnetic core for the inductor structure.

FIG. 4A is a schematic top view showing a power conductor structureaccording to another embodiment of the present invention. FIG. 4B is aschematic cross-sectional view along line I-I′ showing the powerconductor structure of FIG. 4A.

In FIG. 4A, the package substrate 400 is a four-layered PCB having atleast a top metal layer 400 b and a bottom metal layer 400 crespectively disposed on two opposites surfaces of the dielectric core400 a. The dielectric core 400 a may further include more metal layersor interconnecting structures therein. The top metal layer 400 b of thepackage substrate 400 includes a plurality of bond finger pairs 402 onthe top surface 40 a, while the bottom metal layer 400 c includes aplurality of conductive lines 405 on the bottom surface 40 b. Thedielectric core 400 a includes a plurality of conductive vias 403connecting the bond finger pairs 402 and the conductive lines 405.Similarly, each bond finger pair 402 consists of two separate widenportions 402 a located at two sides of the magnetic material block 408,and the two separate widen portions 402 a of each bond finger pair 402are connected through conductive vias 403 inside the dielectric core 400a and one conductive line 405 on the bottom surface 40 b of the packagesubstrate 400. In addition to the bond finger pairs 402, connectiontraces 404 can be arranged beside the most peripheral bond finger pairs402 for electrical connection to external circuits or components.

As shown in FIGS. 4A-4B, a plurality of wires 406 are formed over themagnetic material block 408, between the widen portions 402 a of thebond finger pairs 402 as well as between the widen portions 402 a andthe connection traces 404.

Different from the above embodiment, a trench 412 is formed within thedielectric core 400 a of the package substrate 400. The magneticmaterial block 408 is disposed within the trench 412, below the wires406. Preferably, the magnetic material block 408 is partially protrudedfrom the trench 412 and is higher than the top surface 40 a of thepackage substrate 400. The size of the magnetic material block 408 canbe varied, depending on the desirable module height or the requiredinductance. Accordingly, the depth of the trench 412 may be adjustedbased on the thickness of the package substrate or the desirable moduleheight. For example, when the magnetic material block of a larger sizeis applied, a deeper trench can be formed if a thinner package module isdesirable. From the top view, the magnetic material block 408 isdisposed between the widen portions 402 a of the bond finger pairs 402.One adhesive layer 410 is respectively formed on both opposite surfacesof the magnetic material block 408 to enhance the adhesion between themagnetic material block 408 and the substrate 400 as well as between themagnetic material block 408 and the wires 406.

As embedded within the wiring board or the printed circuit board, eitherthe height of the power inductor structure can be decreased or the powerinductor structure can offer higher inductance values and/or endurehigher currents.

For the exemplary inductor structure shown in FIGS. 1A-1B, through theelectrical connections of the wires and the bond finger pairs, acontinuous coil is obtained. Alternatively, for the exemplary inductorstructures shown in FIGS. 2A-4B, a continuous coil is obtained throughthe electrical connections of the wires, the vias, the conductive linesand the bond finger pairs. The inductance of the exemplary inductorstructures can be calculated according to the following equation:

$L = {\frac{N^{2}\mu\; A}{l}\lbrack H\rbrack}$where L represents inductance in henries (H) of the inductor structure,N represents the number of wire turns of the coil, μ represents thepermeability of the core, l represents the length of the coil and Arepresents the cross-sectional area of the inductor structure (i.e. thearea of core A as shown in FIG. 1B, 2B, 3B or 4B).

Clearly, the inductance of the inductor structure is proportional to theN (the number of wire turns of the coil), μ (the permeability of thecore) and A (the cross-sectional area of the coil). Relatively, theinductor structure of FIG. 2B, 3B or 4B has a cross-sectional area ofthe coil larger than that of the inductor structure of FIG. 1B, becausethe cross-sectional area of the coil includes at least a part of thepackage substrate. In this case, the cross-sectional area of the coil Ais increased and the inductance is increased accordingly. Similarly, forthe layout design of the inductor structure of the present invention, itis acceptable to vary the number of wire turns of the coil N or thelength of the coil l, in order to match suitable electrical properties.Alternatively, the permeability of the magnetic core μ can be modifiedby way of the design of the slot, for example.

Taking the exemplary inductor structure shown in FIGS. 1A-1B as anexample, the inductance is about 2 μH, if the magnetic material isferrite, the permeability of the magnetic core μ is 100 H·m⁻¹, N is 25,and l is 3.6 mm In fact, when compared with the conventional SMT powerinductors, either the inductor structures of FIG. 2A-4B or the inductorstructure of FIGS. 1A-1B can provide comparable satisfactory inductance(e.g. 0.4-5 μH), high current (e.g. 5-15 A) under the applicationfrequency of 10 MHz or lower, as well as with smaller sizes.

In summary, the power inductor structures of the present invention canprovide satisfactory inductance and afford smaller package sizes.Moreover, since there is no need to replace the commonly used packagematerials and the manufacturing processes are compatible with thepresent packaging processes, the fabrication costs can be lower.

Accordingly, the designs disclosed in the present invention areapplicable for power inductor structures as DC to DC converters inpackage structures.

Although the present invention has been disclosed above by theembodiments, they are not intended to limit the present invention.Anybody skilled in the art can make some modifications and alterationwithout departing from the spirit and scope of the present invention.Therefore, the protecting range of the present invention falls in theappended claims.

1. A power inductor structure, comprising: a package substrate having afirst metal layer and a second metal layer respectively disposed on atwo opposite surfaces of the package substrate and a dielectirc coredisposed between the first and second metal layers, wherein the firstmetal layer comprises a plurality of bond finger pairs, while the secondmetal layer comprises a plurality of conductive lines, each bond fingerpair consists of two separate widen portions; a plurality of conductivevias, located within the package substrate and connecting the widenportions of the bond finger pairs and the plurality of the conductivelines, wherein the two widen portions of each bond finger pair iselectrically connected through the conductive vias and one conductiveline; a magnetic material block, located on the package substrate andbetween the widen portions, wherein the magnetic block is located on atop surface of the dielectric core and located above and surrounded by aring-shaped slot concave into the dielectric core; and a plurality ofwires, located over the package substrate and across the magneticmaterial block, and electrically connecting the plurality of the bondfinger pairs.
 2. The power inductor structure as claimed in claim 1,further comprising a first adhesive layer disposed between the magneticmaterial block and the plurality of the wires and a second adhesivelayer disposed between the magnetic material block and the packagesubstrate.
 3. The power inductor structure as claimed in claim 1,wherein the magnetic material block is disposed within a trench of thedielectric core.
 4. The power inductor structure as claimed in claim 3,wherein the magnetic material block is protruded from the trench and ishigher than a top surface of the package substrate.
 5. The powerinductor structure as claimed in claim 1, wherein a material of themagnetic material block includes nickel or a ferrite.
 6. The powerinductor structure as claimed in claim 2, wherein a material of thefirst or second adhesive layer includes a non-conductive epoxy resin. 7.The power inductor structure as claimed in claim 1, wherein the firstmetal layer further comprises at least two connection traceselectrically connecting to the most peripheral bond finger pairs.
 8. Apower inductor, comprising: a package substrate having a dielectriclayer having a first surface and a second surface opposite to the firstsurface, a first metal layer disposed on the first surface of thedielectric layer, and a second metal layer disposed on the secondsurface of the dielectric layer, wherein the first metal layer comprisesa plurality of bond finger pairs, while the second metal layer comprisesa plurality of conductive lines, each bond finger pair consists of twoseparate widen portions; a plurality of conductive vias, located withinthe dielectric layer and connecting the widen portions of the bondfinger pairs and the plurality of the conductive lines, wherein the twowiden portions of each bond finger pair is electrically connectedthrough the conductive vias and one conductive line; a magnetic materialblock, located on the first surface of the dielectric layer and betweenthe widen portions, wherein an adhesive layer is disposed between themagnetic material block and the first surface of the dielectric layer; aring-shaped slot located within the dielectric layer and surrounding themagnetic material block; and a plurality of wires, located over thepackage substrate and across the magnetic material block, andelectrically connecting the plurality of the bond finger pairs.
 9. Thepower inductor as claimed in claim 8, wherein the magnetic materialblock is disposed within a trench of the dielectric core.
 10. The powerinductor as claimed in claim 8, wherein the magnetic material block isprotruded from the trench and is higher than the first surface of thedielectric layer.
 11. The power inductor as claimed in claim 8, whereina material of the magnetic material block includes a nickel or aferrite.
 12. The power inductor as claimed in claim 8, wherein amaterial of the adhesive layer includes a non-conductive epoxy resin.13. The power inductor as claimed in claim 8, wherein the first metallayer further comprises at least two connection traces electricallyconnecting to the most peripheral bond finger pairs.